Caption: Artificial bismuth crystals. Synthetically produced 'hopper crystals' of bismuth. The extravagant colours result from a thin oxidation layer that forms on the surface of these crystals during the formation process. The process involves heating and melting bismuth (chemical symbol: Bi) in a stove and letting the melt cool down under controlled conditions. It is a poor conductor of heat and has the greatest resistance to magnetism of all metals. It has properties similar to lead and it is used extensively in industry, medicine and in chemical catalysts. Each hopper crystal seen here is between 4 and 6 centimetres high.